I would like to write some code on my website where I can do my own stuff, not necessarily forums-related. Some of the stuff that I would like to do involves users having their own accounts to access them, but I don't want to make my site feel split in that you have to have a forums account and an XYZ account for other things on the same site.

If I'm not mistaken, all users are, are information that written down on a database (in a MySQL server, in my case), and that information is checked/modified/written down as needed.

Just for simplicity sake, how do I make my OWN, ground-up, from scratch PHP code for registering a user for the forums? And, I want the user to be able to register on my own custom form, and then go straight to the PHPBB side of the website and be able to login with that same information, straight-up. I know how to use PHP, so I am specifically asking about MySQL information.

If I didn't ask the right questions, or give the right information, what information would you suggest giving me that would help me out?